The invention relates to a connecting element for link chain strands of plough or conveyor chains employed in underground mining, which consists of a central oval round chain member and two separable coupling links each of which consists of a base part having a bore penetrated by the round chain member and an approximately U-shaped suspension part, of which the latter is form-lockingly insertable with its both legs into recesses of the base part and is arrestable therein by a coupling bolt.
The state of the art is documented by a connecting element which has become known in the framework of the German Offenlegungsschrift No. 23 58 308. In this connecting element, the legs of the U-shaped suspension parts are formed in hammerhead-like configurations. The recesses corresponding thereto are then provided one-sidedly in the base parts. Consequently, for connecting the suspension parts with the base parts, the legs have also to be fitted in from one side into the recesses. Subsequently thereto, they are connected by a coupling bolt the cross section of which, however, is considerably smaller than the thickness of the coupling member in the region of the vertical transverse plane.
In the known construction, accordingly, neither the depth of the grooves nor the thickness of the legs reaching into the grooves is equal to the thickness of the coupling members, due to the only one-sidedly performed formation of the grooves. As a result of this, not insignificant cross sections of the base part and of the suspension part are missing for the tensile forces transmission. It has been further established that the uninterrupted fiber flow in the tension direction, which is initially manufactured during forging, is again interrupted by the hammerhead-like recesses and their aftertreatment. Thus, the then still remaining rest cross sections do not suffice in the required degree any longer to offer the necessary resitance to the lasting loads composed of tensile and bending stresses, for the duration of the operation. Breaks and extractions are frequent resulting phenomena.
The one-sided arrangement of the recesses has been established to be unsatisfactory during the practical use even for another reason, though. More particularly, such connecting elements when used in underground mining are by no means subjected only to pure tensile stresses. Rather, transverse forces are additionally exerted on the suspension parts and on the base parts, which aim at bending the coupling members approximately in the region of the coupling bolt connecting the suspension parts with the base parts, relative to each other. As a consequence thereof, the legs of the suspension parts tend to, in turn, emerge out of the one-sidedly provided recesses of the base parts, with the result that the relatively weakly configurated coupling bolt is subjected to high shearing stresses. However, the coupling bolt is no match to these stresses. It becomes destroyed so that the suspension parts necessarily dissociate themselves from the base parts. However, as a result of this, the connecting element falls apart and cannot perform the function entrusted to it any longer. Nevertheless, an increase of the bolt cross section cannot be attended to in that then the rest cross sections of the coupling member which is dependent as to its thickness on the dimension of the round member chain, would be still more reduced and an additional weakening of the transmission of the tensile forces would result therefrom.
It has been further found in connection with the known connecting element that, owing to the permanent frictional contact of the relatively narrow side surfaces of the base parts with the chain guiding tracks in the conveyor or in the plough guide, the material of the base parts is relatively strongly eroded in the region of the side surfaces. As a result of this, the tensile forces transmitting cross sections especially of the base parts become increasingly smaller and smaller and finally lose their function of being able to transmit tensile forces to the required degree altogether.